RECORD: Darwin, C. R. 1838. On the connexion of certain volcanic phænomena, and on the formation of mountain-chains and volcanos, as the effects of continental elevations. [Read 7 March] Proceedings of the Geological Society of London 2: 654-660.

A paper, on the connexion of certain volcanic phænomena, and on the
formation of mountain-chains and volcanos, as the effects of
continental elevations, by Charles Darwin, Esq., Sec. G. S., was then
read.1

The author first gave a detailed account of the volcanic phænomena,
which accompanied the earthquake that destroyed Concepcion on the
morning of the 20th of February, 1835; and then deduced from volcanic
phænomena, certain inferences with respect to the formation of
mountain-chains, and continental elevations.

In describing the phænomena of the earthquake of 1835, Mr. Darwin
quotes the published accounts by Captain Fitzroy* and Mr.

* Journal of the Royal Geographical
Society, vol. vi, p. 319, 1836.2

1 See the revised version of this paper published in the Transactions as Darwin 1840.

Caldcleugh*; likewise communications received by him from Mr.
Douglas,1 a resident on the island of Chiloe.

A few days after the earthquake, several volcanos within the
Cordilleras, to the north of Concepcion, though previously quiescent,
were in great activity. It is doubtful, however, if the volcano of
Antujo, in nearly the latitude of Concepcion, was affected, while the
island of Juan Fernandez, 360 miles to the north-east of the city, was
apparently more violently shaken than the opposite shore of the main
land. Near Bacalao Head, a submarine volcano burst forth in sixty-nine
fathoms water, and continued in action during the day as well as part
of the following night. That island was also affected in a remarkable
manner, by the earthquake which overthrew Concepcion in 1751.

In Concepcion, the undulations of the surface appeared, to the
inhabitants, to proceed from the south-west; and this direction was
likewise inferred, from the effects observed in the buildings; for
those walls, which had their extremities towards the point of
disturbance, remained erect, though much fractured, whilst those (and
the streets cross each other at right angles) which extended parallel
to the line of the vibration, were hurled to the ground. This was
strikingly exemplified in the cathedral, where the great buttresses of
solid brick-work were cut off, as if by a chisel, and thrown down;
while the wall, for the support of which they had been built, though
much shattered, remained standing.

In Chiloe, south of Concepcion, the shocks were very severe, but
they entirely ceased in about eight minutes. The motion, as described
by Mr. Douglas, was horizontal, and similar to that of a ship going
before a high, regular swell; from three to five shocks being felt in a
minute; and the direction being from N.E. to S.W. Forest-trees nearly
touched the soil in these directions; and a pocket compass placed level
on the ground vibrated, during the violent shocks, two points to
westward, but only half a point to eastward; and during the minor
shocks the needle pointed north. At Calbuco, a village on the mainland
opposite the northern extremity of Chiloe, as well as at Valdivia,
between Chiloe and Concepcion, the earthquake was much less severely
felt; and near Mellipulli, in the Cordilleras (not far from Calbuco),
not at all. The volcano of Villareca, near Valdivia, which is said to
be more frequently in irruption than almost any other in the chain, was
not the least affected; though the volcanos of central Chili are stated
by Mr. Caldcleugh to have been seen, some days afterwards, in great
activity. Several of the culminating points of the Cordillera in front
of the island of Chiloe, exhibited increased energy during the
earthquake, and immediately after it. During the shocks, Osorno, which
had been in activity for at least forty-eight hours previously, threw
up a thick column of dark blue smoke; and directly it had passed away,
a large crater was seen forming in the S.S.E. side of the mountain;
Minchinmadiva also, which had been in its usual state of moderate
activity, commenced a fresh period of

violence. At the time of the principal shock, the Corcovado was
quiet; but when the summit of the mountain was visible a week
afterwards, the snow had disappeared from the north-west crater. On
Yntales, to the south of the Corcovado, three black patches, resembling
craters, were observed above the snow-line after the earthquake, though
they had not been noticed previously to it. During the remainder of the
year, the whole of the volcanic chain, from Osorno to Yntales, a range
of 150 miles, exhibited, at times, unusual activity. On the night of
the 11th of November, Osorno and Corcovado threw up stones to a great
height; and on the same day, Talcahuano, the port of Concepcion, 400
miles distant, was shaken by a very severe earthquake; and on the 5th
of December the whole summit of Osorno fell in.

After these details of more particular phænomena, Mr. Darwin alluded
to the great areas over which earthquakes have been simultaneously
felt; but he added, it is impossible even to guess through how wide an
extent, in the subterranean regions, actual changes may have taken
place. In order to enable the reader, who may be more familiar with
European than South American geography, to comprehend the vast surface
which was affected by the earthquake of February 1835, he stated, that
it had a north and south range, equal in extent to the distance between
the North Sea and the Mediterranean: that we must imagine the eastern
coast of England to be permanently raised; and a train of volcanos to
become active in the southern extremity of Norway; also that a
submarine volcano burst forth near the northern extremity of Ireland;
and that the long dormant volcanos of the Cantal and Auvergne, each
sent up a column of smoke.

The contemplation of volcanic phænomena in South America, has
induced the author to infer, that the crust of the globe in Chili rests
on a lake of molten stone, undergoing some slow but great change; for
if this inference be denied, he says, the only alternative is, that
channels from the various points of eruption must unite in some very
deeply-seated focus. This conclusion, however, he doubts, on account of
the union of the different trains of volcanos on the one line of the
Cordillera, and more especially as many hundred square miles of surface
in Chili, have been elevated during the same earthquake. Moreover,
these elevations have acted within a period geologically recent,
throughout the whole, or at least the greater part, of Chili and Peru,
and have upraised the land several hundred feet. He is further of
opinion, that the shocks coming from a given point of the compass, and
the overthrow of the walls, according to their position with respect to
this point, prove that the vibrations do not travel from a profound
depth, but are due to the rending of the strata not far below the
surface of the earth.

In a geological point of view, the author conceives, the three
classes of phænomena exhibited during this earthquake of February 1835,
viz. a submarine outburst—renewed volcanic activity, simultaneously at
distant localities—and a permanent elevation of the land, to be of the
greatest importance, as forming parts of one great action, and

being the effects of one great cause, modified only by local
circumstances. Mr. Darwin further observed, that, as the volcanos near
Chiloe commenced, at the moment of the shock, a period of renewed
activity, which lasted throughout the following year, the motive power
of these volcanos (as well as of the submarine outburst near Juan
Fernandez) must be of a similar nature with that, which, at the same
instant, permanently raised another part of the coast; and he therefore
concluded, that no theory of the cause of volcanos, which is not
applicable to continental elevations, can be considered as
well-grounded.

Mr. Darwin then offered some remarks on the two tables published by
Humboldt,1 of the great earthquakes which affected, in 1797 and 1811, so
large portions of America; and he is of opinion, that a repetition of
the coincidences can alone determine how far the increased activity of
the subterranean powers, at such remote points, was the effect of some
general law, or of accident. He likewise disbelieves that periodical
eruptions, as those of Coseguina, in 1709 and 1809, or of earthquakes,
as the shocks felt at Lima on the 17th of June 1578, and the 17th of
June 1678, are more than accidental agreements. He also gave a table of
the volcanic phænomena in South America in 1835; and concluded, that it
is probable that the subterranean forces manifest, for a period, their
action, beneath a large portion of the South American continent, in the
same intermittent manner as they do beneath isolated volcanos. In the
latter table, Mr. Darwin pointed out the case of Osorno, Aconcagua, and
Coseguina, (the first and last being 2700 miles apart,) which burst
into sudden activity early on the morning of June 20th, 1835; but he
hesitated to assent to there being any necessary connexion between
them. He further remarked, that if such simultaneous outbursts had been
observed in Hecla and Ætna, points unconnected by any uniformity of
physical structure, it would be doubtful how far they would have been
worthy of consideration; but in South America, where the volcanic
orifices fall on one line of uniform, physical structure, and where the
whole country presents proofs of the action of subterranean forces, he
conceives it ceases to be improbable, to any excessive degree, that the
action of the volcanos should sometimes be absolutely simultaneous.

The author then briefly described the groups into which the volcanic
vents of the Cordilleras have been divided. The most southern extends
from Yntales to the volcanos of central Chili, a distance of nearly 800
geographical miles; the second, from Arequipa to Patas, rather more
than 600 miles; the third, from Riobamba to Popayan, a distance of
about 300 miles; and to the northward, there are in Guatimala, Mexico,
and California, three groups of volcanos separated from each other a
few hundred miles. That the vents in each of these groups are
connected, the author has little doubt; but that the groups are united
in one system, there are less satisfactory means of proving.

Mr. Darwin next considered the nature of the earthquakes which occur
at irregular intervals on the South American coast. He is

perfectly convinced, from the numerous points of analogy which exist
between these phænomena and simple eruptions, that they belong to the
same class of events; but he makes this distinction, that earthquakes,
unaccompanied by eruptions at the chief point of disturbance, are
followed by a vast number of minor shocks. These, he believes, indicate
a repeated rending of the strata beneath the surface; whereas, in an
ordinary eruption, a channel is formed during the first outburst.

Among other phænomena belonging to earthquakes, Mr. Darwin alluded
to their affecting elongated areas. Thus the shock in Syria, in 1837,
was felt on a line 500 miles in length by 90 in breadth; and those in
South America are felt along 800 and 1000 miles of coast, but are on no
occasion transmitted across the Cordillera to a nearly equal distance;
and, as a consequence, the inland towns are much less affected than
those near the coast. He does not conceive, however, that the
disturbances proceed from one point, but many ranged in a band,
otherwise the linear extension of earthquakes would be unintelligible.
For instance, in 1835, the island of Chiloe, the neighbourhood of
Concepcion and Juan Fernandez were all violently affected at the same
time.

The last consideration which Mr. Darwin entered upon indicating the
cause of earthquakes, is, that in South America they have been
generally accompanied by elevation of the land; though it is not a
necessary concomitant, at least to a perceptible amount. But he
especially observed, that, as at Concepcion, during the few days
succeeding the great shock, several hundred earthquakes, of no
inconsiderable violence, were experienced, whilst the level of the
ground in that part of the coast certainly was not raised by them (but
after the interval of a few weeks, it stood lower,), there is a clear
indication of some cause of disturbance, independent of the uplifting
of the land in mass.

In summing up the evidence of phænomena accompanying earthquakes,
the author is of opinion that the following conclusions may be drawn:—

1st. That the primary shock of an earthquake is caused by a violent
rending of the strata, which, on the coast of Chili and Peru, seems
generally to occur at the bottom of the neighbouring sea.

2ndly. That this is followed by many minor fractures, which, though
extending upwards, do not, except in submarine volcanos, actually reach
the surface.

3dly. That the area thus fissured extends parallel, or approximately
so, to the neighbouring coast mountains.

Lastly. That the earthquake relieves the subterranean force,
precisely in the same manner as an eruption through an ordinary volcano.

The author afterwards discussed the nature and phænomena of mountain
chains; and stated his belief, that the injection, when in a fluid
state, of the great mass of crystalline matter, of which the axis is
generally composed, would relieve the subterranean pressure

in the same manner as an ejection of lava or scoria; and that the
dislocation of the strata would produce horizontal vibrations through
the surrounding country. In drawing this parallel, he also stated his
belief, that the earthquake of Concepcion marked one step in the
elevation of a mountain chain; and he adduced, in support of this
opinion, the fact observed by Capt. Fitzroy, that the island of Santa
Maria, situated 35 miles to the south-west of that city, was elevated
to three times the height of the upraised coast near Concepcion; or at
the southern extremity of the island, eight feet; in the middle, nine
feet; and at the northern extremity, upwards of ten feet; and that at
Tubal, to the south-east of Santa Maria, the land was raised six feet*;
this unequal change of level indicating, in his opinion, an axis of
elevation in the bottom of the sea, off the northern end of Santa Maria.

Mr. Darwin then alluded to Mr. Hopkins's Researches in Physical
Geology,1 where it is demonstrated, that if an elongated area were
elevated uniformly, it would crack or yield parallel to its longer
axis; and that if the force acted unequally, transverse cracks or
fissures would be produced, and that the masses, thus unequally
disturbed, would represent the irregular outline of a mountain-chain.
He further added, that if the force should act unequally beneath the
area simultaneously affected, various fissures would be formed in
different parts, having different directions, and thus give rise, at
the same moment, to as many local earthquakes. The author believes,
that this view will more readily explain intermediate districts being
little disturbed (as Valdivia in 1835, and in cases alluded to by
Humboldt,) than the supposed inertness of intermediary rock in
conveying the vibrations from a deeply-seated focus.

If the preceding theory of the cause of earthquakes be true, Mr.
Darwin said, we might expect to find, that the many parallel ridges of
which the Cordillera is composed, were of successive ages. In Central
Chili, the only portion examined by him, this is the case, even with
regard to the two main ridges; and some of the exterior lines of
mountains appear, likewise, to be of subsequent dates to the central
ones. The contemplation of these phænomena led him, while in South
America, to infer, that mountain-chains are only subsidiary, and
attendant operations on continental elevations.

The conclusion, that mountain-chains are formed by a long succession
of small movements, the author conceived may be arrived at by
theoretical reasoning. The first effect of disturbing agents, Mr.
Hopkins has shown, is to arch the crust of the earth, and to traverse
it by a system of parallel but vertical fissures; and that subsequent
elevations and subsidences of the disjointed masses would produce
anticlinal and synclinal lines. In the Cordillera, the strata in the
central parts, are inclined at an angle commonly exceeding 45°, and are
very often absolutely vertical, the axis being composed of granitic
masses, which, from the number of dikes branching from them, must have
been fluid when propelled against the lower beds. How then,

he asked, could the strata have been placed in a highly inclined and
often vertical position, by the action of the fluid rock beneath,
without the very bowels of the earth gushing out? If, on the other
hand, it be supposed that mountain-chains were formed by a succession
of shocks similar to those which elevated Concepcion, and after long
intervals, time would be allowed for the injected rock to become solid,
as well as the upper part of the great central mass. Thus, by a
succession of movements, the strata might be placed in any position;
and the crystalline nucleus gradually thickening, would prevent the
surface of the surrounding country, being inundated with molten matter.

In crossing the Andes, Mr. Darwin was surprised at finding, not one
great anticlinal line, but eight, or more; and that the rocks composing
the axes were seldom visible, except in denuded patches in the vallies.
This circumstance, he conceives, must be due to the thickness of the
up-heaved strata being equal, or nearly so, to the average distance of
the anticlinal from the synclinal lines. For in that case, the masses
of strata, when placed vertically, would occupy, or rest on, as great
an horizontal extent, as they did before they were disturbed.

In the central ridges of the Cordillera, there are masses of
compact, unstratified rocks, half again as lofty as Ætna; and these, he
believes, for the reasons before stated, were formed by the gradual
cooling of the subjacent fluid mass; afterwards slowly elevated to the
present position, by the injection of molten matter at nearly as slow a
rate, as we must suppose the innumerable layers of volcanic products,
of which the Sicilian mountain is formed, have been ejected.

In conclusion, Mr. Darwin repeated the argument, that
mountain-chains and volcanos are due to the same cause, and may be
considered as mere subsidiary phænomena, attendant on continental
elevations;—that continental elevations, and the action of volcanos,
are phænomena now in progress, caused by some slow but great change in
the interior of the earth; and, therefore, that it might be
anticipated, that the formation of mountain-chains is likewise in
progress; and at a rate which may be judged of, by either actions, but
most clearly by the growth of volcanos.